Two strains of mice are being used in this project. Female C3H and CBA mice were exposed to a total body dose of radiation of 3 Gy with or without Tempol supplementation in the animal's food. Immediately following the radiation exposure, animals will be placed on either control or Tempol-containing food. The groups include: a) no radiation, control food, b) 3 Gy, control food, c) no radiation, Tempol food, and d) 3 Gy, Tempol food. For C3H mice, one additional group was added receiving 3 Gy total body irradiation where the administration of the Tempol containing food was delayed one month post-irradiation. Animals are checked twice per week for health status and all animals are weighed and food consumption from random cages for each experimental group assessed monthly. The animals will be followed for their entire lifespan (2-3 years) and each animal upon death and/or euthanasia will be necropsied for pathological assessment for cancer. The hypothesis will be tested that mice protected from lethal total body irradiation by administration of a radioprotector immediately before radiation exposure will experience an elevated risk of cancer induction. Mice were exposed to a total body radiation dose of 10.8 Gy, a radiation dose that results in 100% lethality. Ten minutes prior to the 10.8 Gy exposure the animals will be injected with a radioprotector. The control for this group, another set of animals was exposed to 5.4 Gy total body irradiation. This radiation dose was derived from the radiation dose modification factor (2) when the radioprotector is administered 10 min before total body irradiation. These animals will also be followed for their entire lifespan for tumor induction as outlined above.